1. Technical Field
This disclosure generally relates to ink vehicles, ink additives and ink compositions. More particularly, it relates to flexographic ink vehicles, ink additives and flexographic ink compositions with a polymer component having at least two naturally occurring rosins, resins or esters thereof.
2. Related Art
Several printing processes have been developed, and each process generally requires a specific ink composition specially formulated for that particular printing process. The particular ink formulations generally compensate for differing printing conditions between different printing processes and differing print substrates. For example, ink compositions for lithographic printing are considerably different than ink compositions for flexographic printing due in part to different types of printing systems used in the two processes.
Today lithography is generally synonymous with offset lithography. Offset lithography uses water-insoluble ink compositions. Offset lithography printing systems typically include three printing cylinders, an inking system, and a dampening system. The three printing cylinders include a plate cylinder, a blanket cylinder, and an impression cylinder. As the plate cylinder rotates, the plate contacts dampening rollers and then inking rollers. The dampening rollers apply moisture to the non-printing areas of the plate cylinder. Because lithographic inks are immiscible in water, the moisture applied by the dampening systems helps keep the lithographic ink from coating the non-printing areas of the plate. The printing areas of the plate cylinder are generally inked with an oil-based ink composition. The water-insoluble ink composition cannot bleed into the moistened non-printing areas of the plate cylinder.
In contrast, flexographic printing processes use water-based or solvent based ink compositions. Flexographic printing systems are generally systems having rubber or photopolymer plates, reverse-angle doctor blades, and ceramic anilox rollers in central impression cylinder presses. Flexographic presses can be used to print books, newspaper inserts, and packaging materials. Because flexographic printing systems can use water soluble or water-based ink compositions which are less expensive than oil-based ink compositions, flexographic printing typically costs less than lithographic printing. Despite the lower cost of water-soluble ink compositions, the use of these water-based inks does have its share of problems.
For example, current water-based ink compositions often contribute to “Ghosting”. “Ghosting” is an unwanted condition that occurs when an image on a press sheet also appears faintly elsewhere on the same press sheet. Other flexographic inks have poor gloss, increased solids in wastewater streams, poor transferability, and rewetting problems, among others.
Current methods for solving problems related to flexographic printing of water-based ink compositions include increasing pigment concentration in the ink composition and/or using finer pigments. These approaches tend to increase the cost of the ink and have not proven successful in overcoming the problems with current inks, particularly ghosting.
Accordingly, there is a need for improved flexographic ink compositions and flexographic ink vehicles.